The find shows that arthropods—animals such as insects, spiders, and crabs, which have hard external skeletons, jointed limbs, and segmented bodies—once grew much larger than previously thought, said paleobiologist Simon Braddy of the University of Bristol in the United Kingdom.

"This is an amazing discovery," Braddy said.

"We have known for some time that the fossil record yields monster millipedes, supersized scorpions, colossal cockroaches, and jumbo dragonflies," he added. "But we never realized, until now, just how big some of these ancient creepy-crawlies were."

The newfound fossil creature is estimated to be at least one and a half feet (46 centimeters) longer than any previously known prehistoric sea scorpion, a group called eurypterids.

Braddy and co-author Markus Poschmann of the Mainz Museum in Germany report the find in the latest issue of the journal Biology Letters.

Poschmann uncovered the fossilized claw in a quarry near Prüm in Germany.

Rock layers encasing it suggest the creature lived in a brackish coastal swamp or river delta, the researchers said.

Water Bug

Smaller sea scorpions are known to have crawled ashore to mate or shed their outer skins. But "there's no way this monster bug would have been able to do that, because it was just too big," Braddy said.